1. Field of the Invention
The invention relates to fluid dispensing apparatus and method for dispensing liquids; and, more particularly, to a membrane actuated fluid dispenser for delivering the fluid through a plurality of pipettes.
2. Related Art
Dispensing apparatuses capable of simultaneously delivering fluid through a plurality of pipettes are well known in the art. One such example is shown in U.S. Pat. No. 3,572,552, to Guinn and No. 3,807,235 to Lefkovits. Both patents use vacuum or pressure only which does not address the diaphragm (membrane) sag problem. When an elastic membrane is clamped down, it attempts to squeeze into available voids. The cavities are available voids and the excess membrane material bunches up in the cavity and sometimes wrinkles and sags into the cavity. This adversely affects the accuracy of the dispensed volume.
In addition, diaphragm blockage of holes is a problem with certain cavity shapes and hole locations. These patents that use a flat surface immediately above or below the cavity are subject to this. When the diaphragm wrinkles or sags, then vacuum or pressure is applied, if the diaphragm has a sag or wrinkle near the hole then the wrinkle or sag gets forced over the hole, thus blocking its operation.
There is an uneven sealing towards the center of the array of cavities that results when a membrane is peripherally clamped between two large flat plates. It is difficult to seal such an arrangement because the large forces required will bend the plates and they will actually lift up in the center, thus unsealing the center cavities.
Membranes that conform to the shape of the chamber as in these prior art patents forego the possibility of variable volume dispensing.
The use of fixed dispensing needles makes cleaning and contamination control much more difficult.
such prior art devices allows the dispensed fluid to enter the cavity. This makes it difficult to clean and control contamination.
There is thus a need for a fluid dispenser which dispenses a liquid through one or more pipettes in a controlled manner.